The representation of human chromosomes has been carried out so far with banding techniques which permit a specific recognition of the chromosomes using light and dark bands (e.g. G-banding, O-banding, R-banding). These banding techniques are based on methods developed by Caspersson et al., (Exp. Cell Res. 80, 1970, 315–319), Sumner et al. (Nature 232, 1971, 31), Seabright et al. (Lancet 2, 1971, 971–972) and Dutrillaux et al. (C R Acad. Sci., Paris, 272, 1971, 3636–3640). However, the identity of individual chromosomal bands can not be defined in every instance with these methods since all bands of all chromosomes appear only either light or dark. This turns out to be a significant disadvantage since chromosomes can be very different morphologically from cell to cell and from tissue to tissue and can possibly comprise translocations (e.g., in the case of tumors) the recognition of which can be of particular significance for the person to be examined. This applies, e.g., to the decision whether or not to have children in the case of a parent having balanced translocations (“crossing-overs” or “exchanges of parts of chromosomes”), to the recognition of the cause of abnormalities in children with and without mental retardation, and to the diagnosis of leukemias and other tumors which frequently exhibit specific chromosomal changes with diagnostic and therapeutic significance.
Fluorescence in-situ hybridization (FISH) was described for the first time for routine use in practicable form by Pinkel et al. (Proc. Natl. Acad. Sci. USA 83, 1986, 2934–2938) as a suggestion for solving this problem. Today, all human chromosomes of a metaphase can be represented in different colors with this method by using chromosome-specific DNA libraries (chromosome painting, 24-color FISH, Schröck et al., Science 273, 1996, 496497; Speicher et al., Nature Genet. 12, 1996, 368–376). Through the use of vectors, e.g., cosmids, pacs or YACs, which can contain different amount of human DNA, specific chromosomal regions can be re-checked with respect to their integrity via multicolor techniques by means of FISH. Even parts of genes and repetitive DNA elements can be identified in this way regarding their chromosomal localization and their presence or absence. However, a multicolor representation of chromosomal sections at the band level has not been possible so far.
Thus, the problem underlying the current invention is to provide a novel and improved method for the identification of, in particular, changes in chromosomal DNA which method enables a multicolor representation at the band level.
This problem is solved by the embodiments of the present invention characterized in the claims.